fix: master heartbeat not visible to workers in shared MariaDB mode

When master uses SQLite locally, updateNodeState only wrote to local DB.
Workers querying shared MariaDB never saw the master's heartbeat.

Now master also writes its heartbeat to the shared MariaDB via a
temporary connection when MariaDB connection settings are configured.

Bump version to v1.6.4.

config/version

@@ -1 +1 @@
-v1.6.3
+v1.6.4

web/service/node_sync.go

@@ -40,11 +40,12 @@ func NewNodeSyncService() *NodeSyncService {
 
 func (s *NodeSyncService) updateNodeState(version int64, syncErr error, didSync bool) {
 	nodeCfg := config.GetNodeConfigFromJSON()
+	if nodeCfg.NodeID == "" {
+		return
+	}
 	now := time.Now().Unix()
 	state := &model.NodeState{}
-	if nodeCfg.NodeID != "" {
-		_ = database.GetDB().First(state, "node_id = ?", nodeCfg.NodeID).Error
-	}
+	_ = database.GetDB().First(state, "node_id = ?", nodeCfg.NodeID).Error
 	state.NodeID = nodeCfg.NodeID
 	state.NodeRole = string(nodeCfg.Role)
 	state.LastHeartbeatAt = now
@@ -58,6 +59,30 @@ func (s *NodeSyncService) updateNodeState(version int64, syncErr error, didSync
 		state.LastError = ""
 	}
 	_ = database.UpsertNodeState(database.GetDB(), state)
+
+	// Master also writes heartbeat to shared MariaDB so workers can see it
+	if nodeCfg.Role == config.NodeRoleMaster {
+		s.writeStateToSharedMariaDB(state)
+	}
+}
+
+// writeStateToSharedMariaDB opens a temporary connection to the shared
+// MariaDB and upserts the given node state. This is needed when the master
+// uses SQLite locally but workers query the shared MariaDB for heartbeats.
+func (s *NodeSyncService) writeStateToSharedMariaDB(state *model.NodeState) {
+	dbConfig := config.GetDBConfigFromJSON()
+	// Only attempt shared write if MariaDB connection settings are configured.
+	// dbUser is the most reliable indicator — it has no default value.
+	if dbConfig.User == "" || dbConfig.Host == "" {
+		return
+	}
+	sharedDB, err := database.OpenMariaDB(dbConfig)
+	if err != nil {
+		return
+	}
+	sqlDB, _ := sharedDB.DB()
+	defer sqlDB.Close()
+	_ = database.UpsertNodeState(sharedDB, state)
 }
 
 func (s *NodeSyncService) BootstrapFromCache() error {